Project Summary/ Abstract Defective regulation of the immune system is central to the development and progression of T1D. Multiple mechanisms are responsible for maintaining tolerance, including regulatory T cells. Our work has identified that two mechanisms by which Treg fail in T1D subjects;the resistance of effector T cells to suppression and 2)a loss of Treg fitness due to impaired IL-2R signaling. Both of these observations have been made in individuals with longstanding disease what point in time these regulatory defects develop in T1D subjects. In order to understand the role of these regulatory defects in the pathogenesis of T1D and guide the development of therapeutics targeting these defects, a better understanding of the point at which these occur in the Natural History of T1D is required. Our group has established reliable, reproducible assays that can be performed on previously frozen PBMC to address the level of effector T cell resistance to suppression and to address IL-2R signaling. In this grant we propose to examine samples obtained by TrialNet to assess when Teff resistance to Treg or impaired IL-2R signaling occurs during the course of disease from pre-clinical through clinical diagnosis and whether these defects predict subsequent disease course. We will then address these questions in the setting of clinical trials. Specifically, we will address three hypothesis using samples available through TrialNet: 1) Does Teff resistance contribute to the development or the progression of T1D? 2) Does impaired IL-2R signaling contribute to the development and progression of T1D? 3) Does the reversal of Teff resistance correlates with a therapeutic response in clinical trials. To include: MMF/DZB, rituximab, and in the future 1CD3? PUBLIC HEALTH RELEVANCE: Project Narrative This project will define the point at which impaired immune regulation can be detected in individuals with T1D. Based on these findings we will then examine the question, "Can we enhance immune regulation in these individuals with immunotherapy?" We will further determine whether, based on the function of immune regulatory mechanisms in an individual, if they will develop T1D and/ or respond to a specific therapy.